Recovery of selenium



Patented July 21, 1936 PATENT nncovnmz OF snLaNIUM Frank F. Poland, New BrunswiclnN. J., assignor to American Smelting and Refining Company, "New York, N. Y., a corporation of New Jersey No Drawing, 7 Application March a, 1934, Serial No. 114,635

2 Claims. (C1. 23-209) This invention relates to the treatment of ores, metallurgical by-products, residues and similar materials, such as slimes, sludges, anode mud and the like, for the separation and recovery of values contained therein and provides a method. of particular importance in the recovery of selenium from more or less complex mixtures containing various other elements including the noble or precious metals.

In addition to providing a method by which practically all of the selenium present in materials such'as above described may be readily and economically separated and recovered, the invention also facilitates the recovery of other constituents. For example, the bulk of any tellurium present may be readily removed along with the selenium. Further, the period of time during which the noble metals are tied up in the recovery process is materially reduced.

.In accordance with the invention, the material is treated in a manner calculated to convert the entire seleniumcontent to selenite in solution. A separation is then effected between the selenite solution and insoluble constituents including all of the precious metal values following which elemental selenium is readily recovered from the solution. In order to efiect the desired concentration of the selenium as selenite in solution, the invention contemplates subjecting the raw material to controlled oxidation, the degree of same being such that the selenium is oxidized to selenite (ous state) but not to selenate (10 state). By conducting the oxidation in the presence of suitable alkali compounds, the selenium is converted and concentrated practically in toto, as alkali selenite in solution. A separation is then effected in alkaline solution between the soluble and the insoluble constituents and each thereafter separately treated for the recovery of values respectively contained therein.

The following description directed to the treatment of anode mud produced in the electrolytic refining of copper is set forth to more fully and clearly illustrate one manner in which the invention may be practised. The flow-sheet illustrates one manner in which the invention may be practiced.

After suitably treating the anode mud in a roasting furnace to render the copper soluble in dilute acid, the copper may be dissolved and removed in acid solution by agitating the roasted mud in a 15% to 20% solution of sulfuric acid: or copper refining electrolyte, which contains substantial amounts of free sulphuric acid. may be appropriate amount of water, for example, nine used as the leaching medium. The solution may then be decanted off and the residue washed with water and filtered, after which the acid and wash water are preferably processed for the recovery of copper and acid. The following table shows theanalysis of. a typical residue or filter cake:

Per cent Antimony 2.20 Arsenic l; 1.58 Bismuth 0.07 Copper 4.17 Lead 11 17 Nickel 0 .03 Precious'metals (Ag, Au, Pd, Pt) 3 9.6 Selenium 13.78 Sulfur' 3.55 Tellurium 2.44 Tin .38

Following the removal of the copper, the filter 20 cake is preferably dried and ground and then subjected to the controlled oxidizing -treatment con templated by the invention. This treatment may be effected by mixing the material with appropriate quantities of a solid oxidizing agent such as sodium nitrate and incorporating the'resultant mixture in molten sodium hydroxide. While the amount of sodium nitrate necessary to oxidize the selenium to the -ous state but not to the -ic state will depend upon the composition of the material treated, it may be said that in the case of a filter cake of the approximate analysis shown in the preceding table, practically a total separation of selenium may be obtained by mixing the material with an amount of sodium nitrate equal to approximately 12%. by weight of the slimes treated and fusing the mixture with approximately an equal weight of sodium hydroxide within a temperature range of from 900 F. to 1200 F.

When the fusion of the slimes-sodium nitrate mixture and the molten caustic is complete. the whole mass is carefully and slowly added to an cubic feet for each one hundred pounds of'slimes treated.

the caustic solution and impure dor are: u

a Caustic solution Sodium hydroxiderd. 150.0

Selenium (ous) 7 Preoious metals (Ag,

' ImLpure dorv Precious metals (Ag, Au, Pd, Pt);-

15 fIJead 5:25-

Antimony "2.03 Copper; Tellurium 0.13 Selenium. 0 01 20 Arsenic """OiOIf' Thealkailior causticsolutionisivhen neutralized with sulfuric acid" to; p'rc'ibit'ate such elements men-mama; an'd 'lead"; filtered, the neutral solu tion acidified with s'ulfu1fie,-acid'a.n'd' treated with sulfur; (iioxi 'de'*tofpifeoipitatev red selenium; which Grams per liter ,zwhich they are used should be such that the trolled oxidation of the selenium to theous' state, the use of other reagents is within the" scope of the invention; For example, other oxidizing agents including air' may 'be substituted for the sodium nitrate and other alkali comf pounds, for example, soda ash, may be 'used in 7 place of; sodium hydroxide. Also, equivalent po-' tassiumr salts may be employed ifj desired." In. any eveht'j'the reagentaand the quantities in selenium is fully oxidized to the'ous state witha upon boiling with-water yields rblack seleriium neadyjfor market.

a; 1 V impure Qdor after wgs'hmggvii water H 5Q ,mey be agitated with'hot dilute sulfuric acidwhich removes,the"remainingcopper;traces of selenium. and luri m, a any sodium umpourids: not

removed during the Washing'step. ,Theldor, may 7 J melted down using a very small amount; of; a I g s diu hxd ox efo i m= rat fluxw mw mately 99% goldand silver andiwhioh mayibe; readily parted asdesiredm The small amount of slag produced in the melting stepsisgenerallyrich inflead and antimony and may be sent. to theladrefineri"--- 7 j r sul aoido hor ally analy ing anpr x-l While the use'of sodium nitrate and-swam 'hydroicide has been described" to effect the fcori have been disclosed and are pointed out in'the ihtrvening high' temperatand so Controlling the oxidation that theselenium due; and: precipitating selenium" from the sold-- 'ti'on' thereby' reoovering substantially'jth'ei entire. seienium-ooptent of the originalmateriallasj one l outappreci'able quantities thereof. being oxidized to the ic state" 7 r .While eertai'n novel features of the invention annexed. claims, it will be understood'that vari- "=-ous omissions, substitutions and changes may be made-by those skilled in the art without departfron} the spirit of the invention. g What is claimed is;

pf'b'cess fortreatlng ano'de'mud,1 s ines, sludges and theiik'e which contain copp ehnse r leniluhr and precious metals, "which geompriSs leaching: same to remove popper; and without mgthe residue-containing w I I V I na l-sele'riium content a'h'd pr'e'qious 'metals'" to 'oxidationin the presen'cefof moltenicaustic alkali;

is eon verted'iin-" tot'o to jallga li fselen ite 'withojut' the jorination ,of 1 any substantial amountsjgfot le a'te lea ng: he res ltan s on prod ct whereby the alkalisel'e'nitfe enters into fsjoliitioii and thef precious metalsremainj as 'insolubl'e'resicmwmcm: or qqmmcmmn. PatehtNo. 2,c 4a,e63. Jui 21, 19:56.

' v m1. 20mm.

It is hereby certified that error appears in the above numbered patent re uiring correction as follows: In the heading to the printed specification, line 6; strike out the words and. period "No Drawing-H and: insert the following flow sheet as a. part of the patent 01/0/25 JUfF/f/ENHY/Ma/Ydx) m PRESENCE 0F 01 751v (Ill/571C Ill/(flu 70 awrmr .Se 70 Jam/rs lit/T N07 T0 sat/Mrs I rus/ w mam/c7 '15/10/ mm m IVEl/TAWL/Zf n'm/ 1/2604 flan/fr mm 1/ 50 Eco Shaw/0M INVENTOR and that .2 re said. Letters Patent ahouldbe read with these correc tiers therein that the same may cunfom to the-record o'f'the case in the Patent Office Signed and. sealed' this am a of September, A. n. 1235.

Leslie Frazer (Seal) v 7 Acting Cominioner of Patents. 

